[Stoves] Useful Crispin comments at Servals

[Paul Anderson]

Crispin,

Thanks for your efforts at Servals and for your insights and comments.   
I am sending this and your message to others who are working on the rice 
husk gasifier, and TLUDs in general.   We all need to evaluate your 
comments and make and test adjustments. Your combustion analyzer is such 
a great tool !!!!

Note to all:   Crispin is the only stove developer that I know who 
regularly and consistently uses a combustion analyzer (about $3K or 
$4K).   There is not one at Aprovecho, CREEC or any other testing center 
as far as I know.   I suspect that Alex English might have one available 
to him, and others who who work on furnaces (not stoves).

Note:  The mentioned rice husk gasifier is a reconstruction at Servals 
of the design provided by Joe James.   As we all know, things made from 
the same set of plans are not necessarily the same.   Strict comparisons 
are not easy, especially when the two units are 10,000 miles apart.

The comment about the sleeve of secondary air surrounding the column of 
rising woodgases seems quite valid.   We (Wendelbo, Anderson, and all 
who subsequently implement the concentrator disk in TLUD stoves) have 
tended to think that the concentration to the center was sufficient to 
get sufficient mixing.   It is certainly more mixing than without a 
concentrator, but mixing can almost always be improved (with some trade 
offs in price, production, etc.)

The work of Jock Gill, Kirk Harris, Julien Winter and others is giving 
new attention to alternatives for improved mixing.   Much work remains 
to be done.

And we do not know (and are not told because of proprietary 
restrictions) if the technical stove studies funded by millions of 
dollars from the GACC and US DOE are looking at such topics.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com

On 9/23/2014 1:15 PM, Crispin Pemberton-Pigott wrote:
>
> Dear Paul
>
> I tested a large rice hull gasifier today at Servals with a combustion 
> analyser and made some changes to the amount of secondary air. They 
> have already made a large change in the design because if very high 
> excess air values (from too much secondary air). This they did by 
> inverting the combustion chamber and closing all the 5mm holes with 
> bolts. Later they removed some of them (now at the bottom) and drilled 
> some 2mm holes near the top.
>
> With the 5mm holes a little open at the bottom and the 2mm's at the 
> top, there is still 180% EA meaning they should remove about 1/3 of 
> the total secondary air still getting in.
>
> The result of the as-much-restricted-as-possible condition (for the 
> secondary/primary split) was a CO/CO2 ratio of 0.14% which is very 
> good. When the EA went down occasionally to 150% it dropped to 0.13% 
> which means it would drop still further if further secondary air 
> reduction was possible.
>
> It seems, and this is the purpose of my note, that whatever model you 
> have for calculating the need for secondary air is putting in far too 
> much. The volume that wold have gone in (as designed) was about 10 
> times what was needed, but my guestimation (had to assume some things 
> in that then calculate based on hole size).
>
> The penetration of the secondary air into the gas stream is a serious 
> issue with the their regular Champion. The flame is unable to burn 
> because there is air entering as a sheet through a ring gap just below 
> the top cap. This is not a good place, and that is not a good way to 
> let it come it. It never mixes with the gas and only provides a sleeve 
> around the central flame then moves away below the pot.
>
> So...I have suggested they try capping the preheater and installing a 
> roughly calculated 16 x 16mm secondary air holes -- large enough to 
> get impetus towards the centre of the gas column and about right to 
> supply the Champion with adequate secondary air (it too was much too 
> high).
>
> The CO/CO2 ratio was about 0.6% for the Champion. Good enough for 
> government work, as they say. It was quite smoky but did not make much 
> CO. The smoke was directly caused by the long flame sheathed in 
> secondary air, then the flame hitting the pot and chilling against it. 
> Surprised there as not more CO. I think the instrument is working fine 
> so it really is making lots of smoke while not making much CO -- Alex 
> English said it was possible and demonstrated it to me once.
>
> I also tested the Servals kerosene burner head and the other one in 
> the market against each other in the same stove. They have about the 
> same performance but the one in the market definitely over-heats the 
> fuel on high power, causing it to decompose thermally leaving free 
> carbon in the gas stream -- blocks the nozzle.  Reproducible effect.  
> They definitely have a better product.
>
> I am heading to Dubai tonight.
>
> Stay well
>
> Crispin
>

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